1. Field of the Invention
This invention relates to an insulating body and, more particularly, to a cellular ceramic insulating body comprising a plurality of rigid cellular ceramic segments adhesively secured to one another by a bonding agent. The bonding agent forms a flexible bond that substantially prevents thermal stress failure in the cellular ceramic insulating body at temperatures up to at least 650.degree. F.
2. Description of the Prior Art
Various insulation materials, compositions, and techniques are known for preventing heat flow to or from an insulated body. U.S. Pat. No. 3,157,204 to Phillips discloses an insulating and protective covering for metallic structures and parts, such as piping, conduits, and containers. In Phillips, a core of substantially rigid, cellular material, such as a foamed vitreous material, is surrounded by a thermoset, synthetic resinous material to provide the requisite insulation.
A method of producing a cellular glass body and the structure produced thereby suitable for use as an insulation material is disclosed in U.S. Pat. No. 3,325,341 to Shannon. In Shannon's method, the outer skins of a plurality of cellular glass pellets are fused together to form a body having interconnected interstitial voids which communicate with the exterior surface of such body. The interconnected voids are impregnated in whole or in part with either an inorganic or organic binder.
U.S. Pat. No. 3,418,399 to Ziegler discloses a method of making an insulating pipe structure wherein thermoplastic structures are positioned around the pipe to be insulated and melted out to form a plenum chamber about the pipe.
A high strength, thermal shock resistant, laminar ceramic insulating body is disclosed in U.S. Pat. No. 3,528,400 to Norwalk. Such body is formed from a plurality of thin alternate layers of magnesia, spinel or mixtures thereof such that no two adjacent layers are of the same material.
A multi-layered insulating pipe coating is disclosed in U.S. Pat. No. 3,614,967 to Royston. In Royston, the pipe is surrounded by a preformed insulation, such as cellular glass. Such preformed insulation is surrounded by a mat, which includes a first layer of heat softening resin, a layer of woven glass fabric surrounding the first resin layer, a second layer of resin, a layer of conductive foil, a third layer of resin, and an outer layer of water impervious plastic film. The overlapping edges of the mat are heat sealed together.
U.S. Pat. No. 3,959,541 to King et al. discloses a composite laminate insulating body including an inner layer and an outer layer of rigid cellular ceramic insulating material having a layer of uniformly woven glass fiber disposed between the inner and outer layers of cellular insulating material and being adhesively joined thereto by use of a rigid gypsum bonding agent.
Special problems and concerns are generally present when a heat source is kept in an elevated temperature range significantly above ambient temperature, such as is common in steam pipes and other high temperature applications. When various composite insulating materials and compositions are subjected to such elevated temperatures, small cracks or fissures usually will form throughout the cellular insulating layer from the thermal stress in such insulating layer.
Siliceous cellular insulations are known to be useful for insulation of equipment and piping over a wide temperature range of about -450.degree. F. to 800.degree. F. because of their impermeability, high strength, incombustibility, and low absorption of liquids. Such siliceous cellular insulations though, because of their high modulus, or rigidity, their significant thermal expansion coefficient, and low heat transmission may be subject to cracking from high thermal stresses produced by rapid changes in temperature.
The tendency of such siliceous cellular insulations to crack, often referred to as thermal shock, is dependent upon many intrinsic and operational factors, such as the rate of temperature change, the configuration of the member to be insulated, and the thickness of the insulation.
A cellular silica can be manufactured to have an expansion coefficient so low that it can substantially resist thermal shock after being placed red-hot into water. However, the melting point and cellulation temperatures of such a cellular silica are generally in excess of 3000.degree. F. Such high temperatures are difficult to maintain economically for large scale production and other problems may be present, such as sublimation of silicon monoxide during manufacturing.
One insulating technique used in high temperature piping applications was coating a single layer cylinder of insulating material, such a cellular glass, on the outside with a reinforced gypsum or mastic coating. While such reinforced cylinder construction did not prevent cracking in the insulating material, the reinforced coating did hold the cracked pieces in place.
In another technique, a layer of fibrous insulation is provided next to a pipe and a layer of cellular insulating material, such as cellular glass, surrounds the fibrous layer.
What is needed, therefore, is a relatively simple cellular ceramic insulating body having good insulating efficiency and being operable to substantially prevent thermally induced cracking therein and maintain physical integrity at temperatures up to at least 650.degree. F., and desirably to about 800.degree. F.